Antibiotic-tolerant populations of <i>E. coli</i> K-12 TG1 biofilms.

<p>Twenty-four-hour biofilms of <i>E. coli</i> TG1 were preformed in M63B1_Gluc and treated for a period of 24 h with concentrations up to 100- and 80-times the MIC values for ticarcillin and ofloxacin, respectively. Untreated controls represent 48 h biofilms in which fresh M63B1_Gluc without antibiotic was added after 24 h, explaining their values above 100%, represented by a dotted line in each panel. Viable cells of the treated biofilm population were quantified by viable cell counts (A and B) and the XTT-reduction assay (C and D) and were compared to numbers obtained prior to antibiotic treatment. % survival (CFU) values are indicated on top of each bar and are means ± standard error of the means (SEM) of at least six replicates.